This invention relates generally to techniques for cleaning a tube disposed in a well. The invention particularly relates to scraping mud and the like from the outside of a tubular member in an oil or gas well before or during a cementing operation, thereby to improve the bond between the cement and the tubular member.
In drilling and completing oil or gas wells, casing is often installed to line at least part of the wellbore. Sometimes a liner is also installed. The liner usually has a smaller diameter than the casing and is often of a flush-joint construction (i.e., there are no outwardly protruding collars at the joints of the liner) so that the liner can be readily lowered into the bore through the casing after the casing has been set. In this configuration, the liner partially overlaps with the casing, but otherwise it extends below the casing into a deeper region of the well.
To fix the casing or the liner in the wellbore, cement is pumped down the central opening through the tubular string defining the casing or liner and back up the annulus between the outside of the string and the wall of the wellbore. To space the string from the wellbore wall and to scrape the wall to ensure the annulus is open around the entire string, centralizer apparatus are attached to the string prior to lowering it into the well. It is important to have the annulus open so that the cement does not channel along only part of the outside of the string, which channeling results in an improper bond whereby leaks between the bore and the string can occur. Such leaks can allow fluid to uncontrollably escape to the surface, thereby possibly creating a hazardous situation; or the leaks can allow communication of fluids between geological zones, thereby possibly detrimentally contaminating one zone with fluid from another. In addition to, or in lieu of, the use of centralizers, sometimes a liner is rotated or reciprocated during a cementing job to prevent channeling.
Despite the possible benefits of centralizers and reciprocation, drilling mud or other materials may be on the tubular member to be cemented in the well. Such materials can adversely affect or prevent good bonding between the cement and the tubular member. It would be desirable to have some type of article or apparatus or method to reliably clean such materials from the tubular member before or during the cementing process.
A product directed to this need has been advertised by Turbeco Inc. under the term "D-MUDDER." This is described as including a wiper element that seals against the tubular member to wipe a mud film from the outer surface of the tubular member. It is believed that such a wiper seal would rapidly deteriorate in the harsh downhole environment of an oil or gas well; therefore, although this advertised "D-MUDDER" product contemplates the problem addressed by the present invention, there is still the need for an improvement in the technique for cleaning a tubular member in a well.